Micellar catalysis of Diels-Alder reactions: substrate positioning in the micelle.
We have studied the kinetics of the Diels-Alder reactions of cyclopentadiene, sorbyl alcohol, and sorbyltrimethylammonium bromide with a series of N-substituted maleimides in micellar media. Micellar rate constants have been determined and were found to be 20-40 times lower than the respective aqueous rate constants. Nevertheless, it was found that upon addition of sodium dodecyl sulfate the observed rate constants could be enhanced up to a factor of about 4. 5. The low micellar rate constants can be attributed to the relatively apolar (water-poor) region of the micelle, in which the reactions take place. NMR experiments indicate that the reactants usually reside near the alpha- or beta-CH2 groups of the surfactant molecules in the micelle. Comparison of the micellar rate constants with rate constants in water/1-propanol mixtures suggests a concentration of water of 10-15 M in the micellar region where the diene and dienophile react.[1]References
- Micellar catalysis of Diels-Alder reactions: substrate positioning in the micelle. Rispens, T., Engberts, J.B. J. Org. Chem. (2002) [Pubmed]
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